1. Field of the Invention
The present invention is concerned with ink-jet ink sets, ink-jet ink tanks, ink-jet recording methods, and ink-jet recording apparatuses.
2. Description of the Related Art
A lot of printers utilize the ink-jet recording method since the method can reduce the cost with compact apparatuses. In the ink-jet recording method, ink is ejected from the ink ejection opening formed by a nozzle, a slit, and porous film. Particularly, the piezo ink-jet method and the thermal ink-jet method are suitable for high-resolution, high-speed printing. The piezo ink-jet method utilizes deformation of a piezoelectric element for ejecting ink. The thermal ink-jet method utilizes boiling of ink upon application of thermal energy, for ejecting ink.
It has become an important issue to heighten the printing speed and printing quality on plain paper. A method has been proposed (for example in Japanese Patent No. 2667401) in order to realize the high-speed and high-quality printing on plain paper. In the method, a liquid including a compound having a cationic group is provided on the surface of a recording medium, the liquid penetrates into the recording medium, and an ink including an anionic dye is provided on the recording medium immediately after the liquid disappears from the surface of the recording medium (all the liquid has penetrated into the medium), so that an image is formed. In this method, however, the optical density of the image is insufficient in some cases if the ink drying time is short. Moreover, the long-term jetting property is insufficient in some cases if the drop amount is small.
An ink-jet colorant has been also proposed (for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2003-55591 and 2003-172815) which comprises complex powdery particles having a particle size of 0.001 to 0.15 μm. This colorant has been proposed in order to improve the coloring property, vividness of the hue, dispersability, and light fastness. In the particles, extender pigment is coated with a uniform layer of an organic pigment. If the colorant is used for high-speed printing on plain paper, however, the optical density is insufficient in some cases.
Another image forming method has been also proposed (for example, in JP-A Nos. 2002-331657 and 2002-331740) in which ink including a colorant and a liquid composition including particles capable of reacting with the colorant are allowed to react on a recording medium. In the method: the particles and the colorant react in the mixture of the ink and the liquid composition; particles on the recording medium which have not been reacted with the colorant are still in the state of a dispersion; the colorant in the ink in a monomolecular state is adsorbed by the surface of the particles; the particles which have adsorbed the colorant aggregate; and the particles which have adsorbed the colorant are fixed to the surface of the recording medium. However, image properties such as the optical density is not improved in some cases when this method is used for high-speed printing.
As described above, the conventional methods fail to simultaneously satisfy the high color developability, suppressed unevenness in the solid image area, high optical density, suppressed feathering, suppressed intercolor bleed, short drying time, and long-term stability.